Preheat oven to 325°F.
To make graham cracker crust: Break up the graham crackers, place in a food processor and process to crumbs. Add the melted butter, sugar and salt and pulse until combined. Press the mixture into the bottom of a 9-inch pie pan, forming an even layer on the bottom, sides and edge. Bake the crust for 10 minutes. Remove from the oven and allow the crust to cool.
To make filling: While the crust is resting, in an electric mixer with the wire whisk attachment, whip the egg yolks and lime zest at high speed until fluffy, or 5 to 6 minutes. Gradually add the condensed milk and continue to whip until thick, 3 to 4 minutes longer. Lower the mixer speed and slowly add the lime juice until incorporated.
Pour the mixture into the crust and bake for 15 minutes, or until the filling has just set. Cool on a wire rack, and then refrigerate for 20 minutes.
To make topping: Whip the cream, confectioners' sugar and vanilla until nearly stiff. Evenly spread the whipped cream on top of the pie, and place in the freezer for 20 minutes prior to serving. Top with shaved white chocolate if desired.